Ten chickens and 2 pigs were fed non-embryonated eggs of Ascaris suum, Trichuris suis and Oesophagostomum dentatum. Each chicken was fed approximately 15000 eggs of each parasite species while approximately 300000 eggs were given to each of the pigs. After passage in chickens 8.3% of O. dentatum eggs were recovered in faeces compared to 61.1% and 41.6% of A. suum and T. suis eggs, respectively. After passage in pigs the percentages were 38.4%, 49.1% and 30.3%, respectively. After embryonation in the laboratory, 1000 eggs of each parasite species having passed through chickens or pigs or having been kept in the laboratory as controls were fed to groups of 6 pigs to check the infectivity. The number of A. suum recovered from pigs was similar in the 3 groups with 34.0, 52.8 and 41.8%, respectively. The recovery of T. suis in the pig passage group was 54.0% which was significantly lower than the recovery in the chicken passage group (81.8%) and the laboratory group (88.0%). The number of O. dentatum recovered was not significantly different among the 3 experimental groups, the percentage recovery being 30.5, 9.2 and 28.5%, respectively. One explanation for the lower infectivity of T. suis in the pig passage group may be that the eggs have been sublethally damaged through their passage. The results demonstrate that chickens and pigs can act as transport hosts for A. suum, T. suis and O. dentatum, and it is highly probable that these domestic animals are able to act also as transport hosts for the human parasite equivalents. This will have important consequences for the environmental and behavioural strategies in human helminth control programmes.